1. Field
The invention is in the field of safety devices for motor vehicles, particularly such devices adapted to warn a driver that he is falling asleep.
2. State of the Art
A number of systems have been developed to warn a driver of a motor vehicle when he is about to fall asleep. Some of these systems have a sensor which is worn by the driver and is responsive to some sleep related psychological phenomenon such as nodding of the driver's head or changes in the driver's pulse rate. Other systems require the driver to wear a special glove. Still other systems require the driver to either squeeze the steering wheel at intervals or to periodically operate other mechanisms attached to the steering wheel.
It has been found that when a person begins to doze, his grip on the steering wheel loosens. Thus, an apparatus which detects this loosening of the driver's grip can provide an effective basis for an alarm to wake the driver.
Systems such as shown in U.S. Pat. Nos. 2,128,916 and 2,575,926 include steering wheels having pressure-responsive switches thereon so that when the steering wheel is squeezed an electrical circuit is either opened or closed. Such devices still leave room for improvement in operability and effectiveness of the alarm.